Field of the Invention
The present invention relates to a brake HILS (hardware-in-the-loop simulation) system for a railway vehicle, and more particularly, to a brake HILS system for a railway vehicle which simulates a brake system of a railway vehicle including a pneumatic brake system implemented with actual hardwares, in combination with a dynamic characteristic model of the vehicle.
Description of the Related Art
Railroad transportation has been considered as 21th century overland transport for mass transport, high speed, and exactness, and as the railroad transportation becomes faster, a brake system for securing safety and reliability has been considered as an important factor.
A brake system for a railway vehicle, which can stop a railway vehicle running at a high speed with large inertia and mass at an exact position and at an exact time, is an important part directly related to the safety of the railway vehicle. Railway vehicles are equipped with various types of brake systems and appropriately combine (that is, blend) and use them in accordance with the speed and braking situations. In braking types of railway vehicles, there are largely electric braking and mechanical braking. In general, in order to brake a railway vehicle, electric braking is generally used at high speeds and mechanical braking is used at low speeds, thereby completely stopping a railway vehicle.
In the mechanical braking, pneumatic braking is commonly used at present. The pneumatic braking is a type that converts an electrical signal according to a braking command into a pneumatic signal, supplies pneumatic pressure to a brake cylinder, presses a wheel or a disc through a caliper using a force generated in response to the signal, and uses a friction force due to the pressing. In detail, an ECU (Electronic Control Unit) calculates a necessary braking force from a braking command signal, a pneumatic signal, and a speed signal, and obtains necessary pneumatic pressure by communicating with a TCU (Traction Control Unit). A current value corresponding to the necessary pneumatic pressure is outputted and transmitted from an ECU to an EP valve (electro-pneumatic valve), the necessary pneumatic pressure is produced, and the pneumatic pressure is transmitted to a brake cylinder through a WSP (wheel slide protection) valve, thereby generating a braking force.
In the pneumatic braking, there are tread braking, disc braking, and wheel disc braking. The tread braking, a way of converting kinetic energy into thermal energy and dispersing it to the air by pressing a brake shoe to the tread of a wheel, has a defect of a large amount of wheel wear. The disc braking, a way of obtaining a braking force by pressing brake pads to both sides of a disc fitted on an axle, needs more parts, but dissipates heat well without wearing a wheel. However, a motor bogie requires a mechanism for transmitting power from a motor to a wheelset, so there is no sufficient space for installing a disc in a motor bogie and accordingly it is difficult to install a disc in a motor bogie. The wheel disc braking is a way of pressing disc materials on both sides of a wheel with brake pads, thereby braking. In general, the wheel disc braking is used for motor bogies and the disc braking is used for trailer bogies.
In the electric braking, there are rheostatic braking, regenerative braking, and eddy current rail braking. The rheostatic braking is a way of using power generation load as a braking force by operating a traction motor temporarily as an AC or a DC power generator, and of discharging the power as heat by sending it to a main resistor. The regenerative braking is a way of using power generation load as a braking force by operating a traction motor as a power generator and of sending back the power to a power supply to reuse it. The regenerative braking is excellent in terms of energy efficiency, so it is usually used for the subway requiring frequent acceleration and deceleration. The eddy current rail braking is a way of using a braking force that is generated by eddy current induced in a rail when a current is applied to an electromagnet above a rail. The eddy current rail braking does not use a mechanical friction force between a wheel and a rail, so it can obtain a braking force larger than an adhesive force, but is difficult to achieve technically.
There are various types of resistance when a train is running. Train resistance is a general term for them, which includes starting resistance, running resistance, grade resistance, and curve resistance. The starting resistance is generated when a train starts and depends on the state of lubrication, and it can be neglected because it rapidly decreases with an increase of vehicle speed. The running resistance includes resistance due to friction between mechanical parts such as bearings, resistance caused by friction between a rail and a tread and proportioned to a speed, and resistance caused by air friction and proportioned to the square of a speed.
Braking of a railway vehicle is achieved basically by an adhesive force between the wheels and rails, so there is a need of deep understanding for a contact model between a wheel and a rail. First, it is required to understand a creepage model of rolling contact, assuming that a rail and a wheel are not rigid bodies, but elastic bodies. Creepage, an index representing a relative sliding speed between a wheel and a rail, as in the following Equation 1, is a dimensionless number that is the ratio of the difference between a wheel speed and a vehicle body speed to a reference speed.
                              Creepage          ⁢                                          ⁢          ξ                =                                            V              rail                        -                          V              wheel                                V                                    [                  Equation          ⁢                                          ⁢          1                ]            
A creepage theory has been introduced by Carter in his paper in 1926, de Parter and Johnson generalized the result by Carter in three dimensions, and Kalker established a theory about a linear relationship between creepage and creep force. Polach established a theory about a non-linear relationship between creepage and creep force.
In the creepage theory, a wheel and a rail are considered as not rigid bodies, but elastic bodies, so a contact portion makes not a point, but an elliptical surface, and it is called a contact patch. When a braking force is applied, a part of the contact patch becomes a stick area and the other part of the contact patch becomes a slip area, so the total effect appears to be a sliding with a relative speed difference between a wheel and a rail. In other words, when a braking force is applied, a difference is generated between the linear speed of the center of a wheel and the circumferential speed of the wheel, so small creepage is generated. If the braking force increases further, entire contact surface slides, and then a coulomb friction force is generated between a wheel and a rail. The creepage theory allows analyzing microphenomenon at a contact patch between elastic bodies, which cannot be explained by Coulomb friction of rigid bodies.
The creepage can be classified into three types; longitudinal creepage, lateral creepage, and spin creepage. The longitudinal creepage, which is the creepage of a contact patch in the movement direction of a vehicle, represents a relative sliding speed in the movement direction of a vehicle and is caused by lateral displacement or a yaw angle change of a wheelset. The lateral creepage, which represents a relative lateral sliding speed of a contact patch, usually appears in running on a curved rail and is influenced by a contact angle with a rail surface. The spin creepage appears in running on a curved rail and represents a sliding angular speed in spinning. When running on a straight rail, the spin creepage is relatively small, as compared with the longitudinal creepage, so it can be neglected.
Braking phenomena including a contact model between a wheel and a rail, are very complicated, and so the performance of braking systems has been improved through both of theoretical analysis and actual tests on railway vehicles. However, braking tests using actual railway vehicles are very limited, and it is almost impossible to perform braking tests using actual railway vehicles for dangerous situations. However, using an HILS (hardware-in-the-loop simulation) system allows experimentations for braking tests under similar environments to actual vehicle tests, as well as experimentations for braking tests under dangerous situations in which actual vehicle tests are impossible.
The advantage of the HILS system is to make it possible to directly test the performance of prototype hardwares and controllers and software logics in a short time with a low cost. That is, it is possible to investigate and evaluate the performance of designed hardware products and software logics with an HILS system under environments similar to those for actual vehicle tests, by simulating expensive and dangerous vehicle running in real-time using a computer and by putting actual hardware products and software logics to be tested as parts of the HILS system. In view of the designed hardwares and logics, the operations and performances of the hardwares and logics can be tested under environments and conditions similar to those of actual vehicle tests.
Various attempts for implementing realistic vehicle simulations and for solving problems related to braking using the HILS system have been made.
The background of the present invention has been disclosed in Korean Patent No. 10-0668911 (Jan. 12, 2007).